Ultrasonic cleaning apparatus



April 9, 1963 s. E. JACKE ET AL ULTRAsoNIc CLEANING APPARATUS Filed May12, 1959 munirsi! I NV EN TOR S 51m/@Mii ,h6/12 a /f/iW/mf//fmz BY @m iA; 62 a A TTORN E YS 3,085,185 ULTRASONIC CLEANING APARATUS Stanley EmilJacke, Stoney Brook, N.Y., and John W.

Collison, Pontiac, Mich., assignors to Detrex Chemical industries, Inc.,Detroit, Mich., a corporation of Mich- Igan Filed May 12, 1959, Ser. No.812,656 3 Claims. (Cl. S18-116) This invention relates to improvementsin ultrasonic cleaning apparatus, and more particularly concernsdegreasing apparatus utilizing a ferroelectric transducer submerged in a-bath ort liquid chlorinated hydrocarbon solvent such astrichlorethylene.

ln certain cleaning and degreasing applications, it is desirable toutilize high temperatures in the ultrasonic bath of liquid chlorinatedhydrocarbon solvent. However, high temperatures adversely affect thepiezoelectric transducer (which may be made of barium titanate) so thatthe transducer depolarizes when the temperature exceeds the Chirie pointof the material from which the transducer is made. Under suchconditions, the expensive transducer is destroyed.

Accordingly, it has been a problem to discover means whereby anultrasonic bath could be operated at high temperatures and yet notdestroy the transducer by depolarization. It has been a problem tooperate at high temperatures without destroying the transducer, and alsoto provide fail-safe means whereby if the system fails, the transduceris protected. 1t has also been a problem to provide means whereby highvoltage and current may be used across the transducer, and at the sametime to provide means whereby a person who may -accidentally come incontact with such high voltages and currents is prevented from beingelectrocuted.

Accordingly, it is an object of this invention to provide ultrasoniccleaning apparatus which solves the foregoing problems.

It is another object of this invention to provide ultrasonic cleaningapparatus which operates safely and ethciently at elevated temperaturesabove the normal Curie point of the material of which lthe transducer ismade without causing depolarization of the transducer.

It is another object of this invention 'to provide ultrasonic cleaningapparatus wherein high voltages and currents are used, and to providemeans for preventing the electrocution of a person who may accidentallycome in contact with said voltages and currents.

4Other objects and advantages of this invention, includingits'simplicity and economy, as Well as the ease with which it may beadapted to existing equipment, will further become apparent hereinafterand in the drawing.

rl`he drawing is a diagrammatic View of ultrasonic cleaning apparatusconstructed in accordance with this invention.

Although specific terms are used in the following description forclarity, these terms are intended to refer only to the structure shownin the drawings and are not intended to define or limit the scope of theinvention.

Turning now .to the specific embodiment of the invention selected forillustration in the drawing, there is shown ultrasonic cleaningapparatus including a well 1 containing a Iliquid chlorinatedhydrocarbon solvent 2 such as trichlorethylene, perchlorethylene, ormethylene chloride. Positioned in the liquid of .the well is anultrasonic transducer 3 which may be made of barium titanate or otherferroelectric transducer material. Transducer 3 may .be constructed inaccordance with the disclosure in U.S. Patent No. 2,802,476 which issuedto T. I. Kearney on August 13, 1957.

Silvered electrodes 4 and 5 of transducer o are conrates Patent ICCnected in an electrical circuit with a biasing supply lcircuit 6 and agenerator control circuit 7 which is actuated by the biasing supplycircuit 6 to control a radio frequency generator 8. Biasing supplycircuit 6 impresses a DC. voltage bias across ultrasonic transducer 3 toenable transducer 3 to operate at elevated temperatures above the normalCurie point of the material from which transducer 3 is made withoutcausing depolarization and deterioration of the expensive transducer.Generator 8 impresses an A.C. voltage on ltransducer 3 to generateultrasonic waves which are useful in cleaning and degreasing operations.Generator control circuit 7 operates to shut off generator 8 when the.biasing supply circuit 6 fails. If the radio frequency generator 8 wereto continue its operation without the D.C. bias supplied by the biasingcircuit 6, transducer 3 would depolarize, deteriorate, and be destroyed.

Biasing supply circuit 6 includes a transformer 11 having a primarywinding i12 connected to a source of power 13, and a secondary winding14. Secondary winding 14 supplies approximately 3000 volts, 60 cycle,A.C. to a selenium rectifier 15 which supplies pulsating D.C. to thefilter network of resistor 16 and capacitors 17-20 which smooth thepulsating D.C. Resistors 2.3-26 form part of a divider network to dividethe voltage evenly across the four filter capacitors 17-20 and therebypermit the use of less expensive elements. The effective ilter capacityis one quarter of the value of capacitor 17 which is large enough toprovide relatively good filtering but is not so large that the timerequired to charge the bank of capacitors 17-20 through the resistor 16becomes too great when the power is turned on.

A resistor 27 is used to provide the system with poor voltage regulationin order to cause the output voltage to drop to a very low value if aperson should accidentally come in contact with the connections totransducer 3. With transducer 3 connected in the circuit and no shortcircuits in the system, the voltage drop across resistor 27 isnegligible. Resistor 27 acts as a series A.C. lter and preventsexcessive alternating current from flowing through a bank of capacitors31-33 instead of through the bank of capacitors 17-20. The resistors34-36 dilvide the D.C. voltage evenly across each of the capacitors31-33.

When power is rst turned on, the bank of capacitors 31-33 permit highenough direct current to flow at the outset to close contacts 37 of anunder voltage relay 38.

lf the capacitors 17-20 are much larger than four microfarads, the bankof capacitors 31-33 charge up at a slower rate so that the under voltagerelay 38 is not energized. The value of the resistors 34-36 are set sothat when the voltage from a point A to ground is above nine hundredvolts, enough direct current flows through coil `4i of under voltagerelay 38 to keep the relay 38 energized (contacts closed). Ilf thevoltage drops below nine hundred volts D.C., under voltage relay 38opens and contacts 37 are opened.

Resistors 34-36 and resistor 4Z form a voltage divider to supply a smallpositive potential to the grid 43 of a thyra-tron tube 44 which ispreferably a 2D2l. As long as the proper bias potential exists ybetweenpoint A and ground, thyratron 44 conducts and keeps the relay 38energized. The contacts 37 of under voltage relay 38 are in the holdingcircuit of the generator control circuit 7, and resistor 42 is providedwith a capacitor 4t) (preferably .O01 microfarad) in parallel therewith.

Resistors `45-47, diodes 48, 49, secondary winding 52 and capacitor 53(preferably .ten microfarads) provide a positive potential for thecathode 54 of thyratron 44 so that the thyratron 44 cuts off fromconduction when the S; transducer biasing potential from point A toground falls below a predetermined value.

Located near the output of generator 8 is a blocking network 55 whichpasses the radio tfrequency energy from generator 3 toward thetransducer 3 but blocks it toward biasing supply circuit 6, and whichpasses the D.C. voltage from the biasing supply circuit 6 toward thetransducer 3 but blocks it from the generator S. Blocking network Sincludes a resistor .56 and capacitors 57-59. Capacitors 5S, 59 blockthe DC. bias voltage from flowing toward generator 8, and resistor 56and capacitor 57 block the radio frequency energy from owing toward thebiasing supply circuit 6.

Capacitor 57 is a radio frequency bypass and is not critical in value.Resistor 56 and capacitor 57 form RF lter (L section) to keep the radiofrequency energy generated by generator 8 from owing back into thedivider networks. Capacitors 58, 59 are coupling capacitors to keep theD.C. bias from owing toward generator 8 and for allowing the radiofrequency to low toward transducer 3. These capacitors should be .0r-1microfarad each or larger to keep the capacitive reactance at this pointrelatively small.

Also provided is a heater circuit which includes secondary winding 61and heater element 62.

Contacts 37 of under voltage relay 3S are in the circuit which includesstop button 63 with its contacts 64, start button 65 with its contacts66, control relay 67 with its coil 68 and contacts 69, and a source ofpower 72.

in operation, the D.C. bias across transducer 3 is above nine hundredvolts, thyratron tube 44 is conducting, under voltage relay 38 isenergized so that its contacts 37 are closed, coil 63 of control relay67 is energized so that its contacts 69 are closed so that power issupplied to generator 3 which puts A.C. energy across transducer 3 togenerate ultrasonic waves.

It the biasing Voltage should fall below nine hundred volts (or otherpredetermined value), thyratron tube 44 stops conducting whichde-energizes the coil 41 of under voltage relay 3S -to open contacts 37.This de-energizes coil 68 of control relay 67 to open contacts 69 to cutott` the .power to generator 8 and thereby shut down the generator.

The system is operated very satisfactorily where resistor 1-6 is 200K,resistors 23-26 are each 72K, resistor 27 is 1K, resistors 3ft-36 areeach 120K, resistor 56 is 10K, capacitors 17-26 are each 4 microfarads,450 volt electrolytic, capacitors .S1-33 are each 8 microfarads, 450volt electrolytic, and capacitor 57 is a .0047 microfarad, 3 kv., discceramic.

-It is to be understood that the form of the invention herewith shownand described is to be taken as a preferred embodiment. Various changesmay be made in the shape, size, and arrangement of parts. For example,equivalent elements may be substituted for those illustrated anddescribed herein, parts may be reversed, and certain features of theinvention may be utilized independently of the use of other features,all without departing from the spirit or scope of the invention as denedin the subjoined claims.

Having thus described our invention, we claim:

1. In ultrasonic cleaning apparatus having a well, a liquid chlorinatedhydrocarbon solvent contained within said well, a piezoelectrictransducer submerged in the solvent of the well, and means for applyinga highfrequency voltage across said transducer to vibrate saidtransducer and to generate ultrasonic waves in said solvent; means foroperating said transducer at high temperatures exceeding the otherwisesafe temperature limits of said transducer material, said lastnamedmeans comprising means for applying a high direct-current biasingvoltage across said transducer; and control means coupled both to saiddirect-current biasing voltage means and also to said high-frequencyvoltage means ttor preventing the application of said high-frequencyvoltage across said transducer unless said direct-current biasingvoltage exceeds a selected minimum value and for removing saidhigh-frequency voltage from said transducerwhen said direct-currentbiasing voltage falls Ibelow a selected minimum value.

2. Apparatus adapted for operating piezoelectric transducers at hightemperatures exceeding the Curie point of the piezoelectric material,said apparatus comprising: a well adapted to contain a high-temperatureliquid chlorinated hydrocarbon solvent; a piezoelectric transducer insaid well; a radio-frequency generator; means coupling the outputterminals of said radio-frequency generator across said transducer; adirect-current generator for developing a high biasing voltage; meansfor applying said high biasing voltage across said transducer; a relayhaving a Winding and contacts; means, including the contacts of saidrelay, for coupling a source orf alternating current power to the inputterminals of said radiofrequency generator for operating said generator;an electronic switch in series with the winding of said relay forcontrolling the ilow of current through said winding; means couplingsaid electronic switch to output terminals of said direct-currentgenerator for controlling the state of said switch according to themagnitude of the directcurrent biasing voltage, said electronic switchbeing adapted to open the series circuit through said relay winding whenthe direct-current voltage applied to said switch is less than aselected minimum.

3. Apparatus as claimed in claim 2 characterized in that said electronicswitch comprises a thyratron tube and means for applying a portion ofsaid direct-current biasing voltage across the input electrodes of saidthyratron for biasing said tube into conduction when said direct-currentbiasing voltage is above said selected minimum value.

References Cited in the le of this patent UNITED STATES PATENTS2,115,582 Jones Apr. 26, 1938 2,683,866 Samsel Iuly 13, 1954 2,714,186Henrich July 26, 1955 2,752,512 Sarratt June 26, 1956 2,799,787 Guttneret al. July 16, 1957 2,814,575 Lange Nov. 26, 1957 2,891,1176 BransonJune 16, 1959 y2,894,176 Hegarty et al July '7, 1959 2,916,266 Pray Dec.8, 1959 FOREIGN PATENTS 575,575 Great Britain Feb. 23, 1946

1. IN ULTRASONIC CLEANING APPARATUS HAVING A WELL, A LIQUID CHLORINATEDHYDROCARBON SOLVENT CONTAINED WITHIN SAID WELL, A PIEZOELECTRICTRANSDUCER SUBMERGED IN THE SOLVENT OF THE WELL, AND MEANS FOR APPLYINGA HIGHFREQUENCY VOLTAGE ACROSS SAID TRANSDUCER TO VIBRATE SAIDTRANSDUCER AND TO GENERATE ULTRASONIC WAVES IN SAID SOLVENT; MEANS FOROPERATING SAID TRANSDUCER AT HIGH TEMPERATURES EXCEEDING THE OTHERWISESAFE TEMPERATURE LIMITS OF SAID TRANSDUCER MATERIAL, SAID LASTNAMEDMEANS COMPRISING MEANS FOR APPLYING A HIGH DIRECT-CURRENT BIASINGVOLTAGE ACROSS SAID TRANSDUCER; AND CONTROL MEANS COUPLED BOTH TO SAIDDIRECT-CURRENT BIASING VOLTAGE MEANS AND ALSO TO SAID HIGH-FREQUENCYVOLTAGE ACROSS SAID TRANSDUCER UNLESS SAID DIRECT-CURRENT BIASINGVOLTAGE EXCEEDS A SELECTED MINIMUM VALUE AND FOR REMOVING SAIDHIGH-FREQUENCY VOLTAGE FROM SAID TRANSDUCER WHEN SAID DIRECT-CURRENTBIASING VOLTAGE FALLS BELOW A SELECTED MINIMUM VALUE.